PHP Syntax. PHP is a great example of a commonly-used modern programming language.

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Rafe McDowell
6 years ago
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2 PHP is a great example of a commonly-used modern programming language. C was first released in 1972, PHP in PHP is an excellent language choice for software that requires an easy way to do things that, in C, are really complicated. String manipulation Networking Fortunately, PHP is heavily inspired by C (in fact, the PHP interpreter is written in C) and so the syntax should be pretty familiar.

3 To start writing PHP, open up a file with the.php file extension. All PHP code inside of that file must be enclosed in the PHP delimiters. <?php?> If not, when the code is run, everything outside of those delimiters will simply be printed out verbatim in your program.

4 Unlike C, which is a compiled language, PHP is an interpreted language. Get to skip the step of compiling our code, with the trade off that PHP code needs to be converted to 0s and 1s on the fly, which might slow the program down. The fact that the PHP interpreter effectively discards non- PHP can actually be used to our advantage though, particularly when we start to mix PHP and HTML in the context of web programming.

5 Variables PHP variables have two big differences from C. No type specifier. All names start with $.

6 Variables PHP variables have two big differences from C. No type specifier. All names start with $. int x = 54;

7 Variables PHP variables have two big differences from C. No type specifier. All names start with $. int x = 54;

8 Variables PHP variables have two big differences from C. No type specifier. All names start with $. $x = 54;

9 Variables PHP variables have two big differences from C. No type specifier. All names start with $. string phrase = This is CS50 ;

10 Variables PHP variables have two big differences from C. No type specifier. All names start with $. string phrase = This is CS50 ;

11 Variables PHP variables have two big differences from C. No type specifier. All names start with $. $phrase = This is CS50 ;

12 Conditionals All of the old favorites from C are still available for you to use.

13 Conditionals All of the old favorites from C are still available for you to use. if ($y < 43 $z == 15) { }

14 Conditionals All of the old favorites from C are still available for you to use. if ($y < 43 $z == 15) { } else { }

15 Conditionals All of the old favorites from C are still available for you to use. if ($coursenum == 50) { } else if ($name == David ) { }

16 Conditionals All of the old favorites from C are still available for you to use. if ($coursenum == 50) { } else if ($name == David ) { }

17 Conditionals All of the old favorites from C are still available for you to use. if ($coursenum == 50) { } elseif ($name == David ) { }

18 Conditionals All of the old favorites from C are still available for you to use. $var = A ; $letter = ctype_alpha($var)? true : false;

19 Conditionals All of the old favorites from C are still available for you to use. $state = readline( Your state, please: ); switch($state) { case MA : case Mass. : case Massachusetts : // stuff break; default: echo( I don t understand your input! ); }

20 Conditionals All of the old favorites from C are still available for you to use. $state = readline( Your state, please: ); switch($state) { case MA : case Mass. : case Massachusetts : // stuff break; default: echo( I don t understand your input! ); }

21 Loops All of the old favorites from C are still available for you to use.

22 Loops All of the old favorites from C are still available for you to use. $counter = 1; while($counter <= 100) { print($counter); $counter++; }

23 Loops All of the old favorites from C are still available for you to use. $counter = 1; do { print($counter); $counter++; } while($counter <= 100);

24 Loops All of the old favorites from C are still available for you to use. for ($counter = 1; $counter <= 100; $counter++) print($counter);

25 Arrays Here s where things really start to get a lot better than C. PHP arrays are not fixed in size; they can grow or shrink as needed, and you can always tack extra elements onto your array and splice things in and out easily. Because PHP is loosely typed, your arrays can also mix different data types together.

26 Arrays Declaring an array is pretty straightforward. $nums = array(1, 2, 3, 4);

27 Arrays Declaring an array is pretty straightforward though there is more than one way to do it. $nums = [1, 2, 3, 4];

28 Arrays Tacking on to an existing array can be done a few ways: $nums = [1, 2, 3, 4]; $nums[4] = 5;

29 Arrays Tacking on to an existing array can be done a few ways: $nums = [1, 2, 3, 4]; $nums[] = 5;

30 Arrays Tacking on to an existing array can be done a few ways: $nums = [1, 2, 3, 4]; array_push($nums, 5);

31 Arrays Recall that our arrays also do not have to always contain elements of the same data type. $nums = [1, true, 3, 4]; array_push($nums, five );

32 Associative arrays PHP also has built in support for associative arrays, allowing you to specify array indices with words or phrases (keys), instead of integers, which you were restricted to in C.

33 Associative arrays $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ];

34 Associative arrays $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ];

35 Associative arrays $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ];

36 Associative arrays $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ];

37 Associative arrays $pizza[ cheese ] = 7.99;

38 Associative arrays $pizza[ cheese ] = 7.99; if ($pizza[ vegetable ] < 12) { }

39 Associative arrays $pizza[ cheese ] = 7.99; if ($pizza[ vegetable ] < 12) { } $pizza[ bacon ] = 13.49;

40 Associative arrays PHP also has built in support for associative arrays, allowing you to specify array indices with words or phrases (keys), instead of integers, which you were restricted to in C. But this creates a somewhat new problem how do we iterate through an associative array? We don t have indexes ranging from [0, n-1] anymore.

41 Loops (redux) PHP also includes a new kind of loop called foreach that allows you to iterate across any array, but is particularly useful for associative arrays. foreach($array as $key) { // use $key in here as a stand-in for $array[$i] }

42 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ];

43 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ]; foreach($pizzas as $pizza) { print($pizza); print( \n ); }

44 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ]; foreach($pizzas as $pizza) { print($pizza); print( \n ); }

45 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ]; foreach($pizzas as $pizza) { print($pizza); print( \n ); }

46 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ]; foreach($pizzas as $topping => $price) { }

47 Loops (redux) $pizzas = [ cheese => 8.99, pepperoni => 9.99, vegetable => 10.99, buffalo chicken => ]; foreach($pizzas as $topping => $price) { print( A whole ); print($topping); print( pizza costs $ ); print($price); print(.\n ); }

48 A whole cheese pizza costs $8.99. A whole pepperoni pizza costs $9.99. A whole vegetable pizza costs $ A whole buffalo chicken pizza costs $11.99.

49 Printing and variable interpolation We ve already seen a few ways to print out information to the user. print() echo() Suffice it to say, PHP has a lot of ways to print, including ways to print out substituted variables in the middle of strings.

50 Printing and variable interpolation print( A whole ); print($topping); print( pizza costs $ ); print($price); print(.\n );

51 Printing and variable interpolation printf( A whole %s pizza costs $%s.\n, $topping, $price);

52 Printing and variable interpolation printf( A whole %s pizza costs $%s.\n, $topping, $price);

53 Printing and variable interpolation echo( A whole {$topping} pizza costs \${$price}.\n );

54 Printing and variable interpolation echo( A whole {$topping} pizza costs \${$price}.\n );

55 Printing and variable interpolation echo( A whole {$topping} pizza costs \${$price}.\n );

56 Printing and variable interpolation print( A whole {$topping} pizza costs \${$price}.\n );

57 Printing and variable interpolation print( A whole. $topping. pizza costs $. $price..\n );

58 Printing and variable interpolation print( A whole. $topping. pizza costs $. $price..\n );

59 Printing and variable interpolation print( A whole. $topping. pizza costs $. $price..\n );

60 Functions PHP has support for functions as well. Like variables, we don t need to specify the return type of the function (because it doesn t matter), nor the data types of any parameters (ditto). All functions are introduced with the function keyword. Also, no need for main(), since the interpreter just reads from top to bottom!

61 Functions function hard_square($x) { $result = 0; for ($i = 0; $i < $x; $i++) $result += $x; return $result; }

62 <?php $x = readline( Give me a number to square: ); echo(hard_square($x). \n );?> function hard_square($x) { $result = 0; for ($i = 0; $i < $x; $i++) $result += $x; return $result; }

63 Functions function hard_square($x = 10) { $result = 0; for ($i = 0; $i < $x; $i++) $result += $x; return $result; }

64 <?php echo(hard_square(). \n );?> function hard_square($x = 10) { $result = 0; for ($i = 0; $i < $x; $i++) $result += $x; return $result; }

65 <?php echo(hard_square(). \n );?> function hard_square($x = 10) { $result = 0; for ($i = 0; $i < $x; $i++) $result += $x; return $result; }

66 Including files Just like C programs can consist of multiple files to form a single program, so can PHP programs tie files together. #include <cs50.h>

67 Including files Just like C programs can consist of multiple files to form a single program, so can PHP programs tie files together. #include <cs50.h>

68 Including files Just like C programs can consist of multiple files to form a single program, so can PHP programs tie files together. require_once( DIR. cs50.php );

69 Including files Just like C programs can consist of multiple files to form a single program, so can PHP programs tie files together. require_once( DIR. cs50.php );

70 Though PHP is primarily used (and was initially designed) as a language for web-based programming, it is a full language and can do nearly all things C can, which means it can be run from the command line. All that is required is that the PHP interpreter is installed on the system you wish to run your PHP programs on.

71 To run your PHP program through the PHP interpreter at the command-line, simply type php <file> and your program will run through the interpreter, which will execute everything inside of the PHP delimiters, and simply print out the rest.

72 Recall that you don t have to have only one set of PHP delimiters in your program. You can have as many as you d like, opening and closing them as needed.

73 You can also make your programs look a lot more like C programs when they execute by adding a shebang to the top of your PHP files, which automatically finds and executes the interpreter for you. #!/usr/bin/php If you do this, you need to change the permissions on your file as well using the linux command chmod as follows: chmod a+x <file>

JavaScript. Like PHP, JavaScript is a modern programming language that is derived from the syntax at C.

JavaScript. Like PHP, JavaScript is a modern programming language that is derived from the syntax at C. Like PHP, JavaScript is a modern programming language that is derived from the syntax at C. It has been around just about as long as PHP, also having been invented in 1995. JavaScript, HTML, and CSS make